The present invention relates to a process for manufacturing a hydrogen and carbon monoxide containing gas by partially combusting a fuel in a reactor, cooling the gas obtained in a waste heat boiler and washing the cooled gas in a scrubber to remove entrained soot particles. More particularly, the invention is directed to an improvement in the above-mentioned conventional process wherein the cooled gas washing step is carried out in a manner such that soot separation occurs more readily and subsequent processing of the gas to remove conventional gaseous contaminants is substantially avoided.
By the partial, i.e., sub-stoichiometric combustion of gaseous liquid or solid hydrocarbonaceous fuel, a gas is obtained that predominantly consists of hydrogen and carbon monoxide. The fuel can be combusted with oxygen and this process may yield a synthesis gas for manufacturing, e.g., methanol or technically pure hydrogen. The carbon monoxide can be converted catalytically with steam to produce a gas containing more hydrogen. If air is used to support the combustion, the gas will contain nitrogen as well and may, for example, be used for manufacturing ammonia or for generating electricity. In the latter case the partial combustion is carried out at elevated pressure and the gas so obtained is usually first expanded through a gas turbine. In other instances, the partial combustion may be carried out at elevated pressures as well.
Generally, the gas that is obtained by partial combustion contains an amount of soot, ash and contaminating gases such as HCN, H.sub.2 S, COS, CS.sub.2 and CO.sub.2.
Depending on the type of fuel and on the operation conditions, amounts of soot of up to 3 or 4%w may be present in the crude gas product emanating from the partial combustion reactor. The soot particles are, in general, very small and cannot easily be removed from the crude gas at the moment the latter leaves the partial combustion reactor due to the high temperature of the gas. Normally, this temperature is higher than 1000.degree. C.
The gas is typically passed from the reactor into a special waste heat boiler, which is designed to withstand the elevated pressures at which the gas is generated and to avoid becoming clogged by the soot contained therein. In a waste heat boiler with helically coiled tubes, for example, the soot is not deposited on the walls of the tubes. High-pressure steam can be generated in the waste heat boiler and the gas may, for example, be cooled to below 400.degree. C.
After this cooling step the soot and other contaminants can be separated from the gas. According to one conventional procedure, the soot particles may, for example, be removed by "quenching" the gas with water in a scrubber in which the soot is washed out and an aqueous soot slurry is obtained. The ash is also taken up by the water. The temperature of the gas is further reduced by this soot removal step.
Subsequently the gaseous contaminants may be absorbed from the gas in an absorber column with the aid of an absorber liquid. Purification of the crude partial combustion gas by this two-step procedure is considered advantageous because contamination of the absorber liquid for gaseous contaminants with soot is avoided by this route.
However, separation of solid and gaseous contaminants in two separate steps is expensive and heat losses unavoidably occur in the process because of the temperature constraints inherent in the gaseous absorption step. Furthermore, the density of the soot obtained in partial combustion is typically rather close to that of water and as a result it is difficult to obtain a good separation of soot from water using conventional separation techniques.
The instant invention provides a process by which the soot and gaseous contaminant removal steps are combined in a single step and the problems associated with separate operation of each step are substantially eliminated.